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Thesis Defense
Superconducting diode effect
Date: Friday, May 2nd
Time: 2:15 pm - 3:45 pm
Place: 2104 CH
Speaker: Jaglul Hasan, Physics PhD student
Abstract: In this thesis, we explore the generalities of the supercurrent diode effect. As an illustrative example, we examine a model of a two-dimensional superconductor with Rashba-type spin-orbit coupling under an in-plane magnetic field and in the clean limit, which realizes a helical phase. First, we utilize Ginzburg-Landau phenomenology to derive a general formula for the diode efficiency. This is achieved by incorporating higher gradient terms in the Lifshitz invariants, which are responsible for the nonreciprocal superflow. Subsequently, we validate these results through microscopic diagrammatic computation and further estimate correction terms arising from interband pairing correlations. We provide a detailed comparison to prior investigations of this problem conducted within the framework of the quasiclassical approximation based on the Eilenberger equation.

Even though superconducting diode effect (SDE) has garnered significant attention due to its potential applications in superconducting electronics, the role of disorder scattering in SDE has rarely been considered, despite its potential qualitative impact, as we demonstrate. We investigate SDE in a disordered Rashba superconductor under an in-plane magnetic field, employing a self-consistent Born approximation to derive the corresponding Ginzburg-Landau theory. Our analysis reveals two surprising effects. First, in the strong Rashba SOC regime, disorder becomes the driving mechanism of SDE, which vanishes in its absence. In this case, we show that disorder-induced mixing of singlet and triplet superconducting orders underlies the effect. Second, in the weak Rashba spin-orbit coupling (SOC) regime, disorder can reverse the direction of the diode effect, indicated by a sign change in the superconducting diode efficiency coefficient.
Host: Alex Levchenko
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